A programmable display device includes a display section for displaying an image, a touch panel for a touch input, an interface for communication with a device connected to the programmable display device, and a control section for controlling the above sections. Such a programmable display device has (i) a function of indicating an operating condition of a device in the form of an image displayed by the display section and (ii) a function of receiving, at the touch panel on the display section, an operational input for providing a control instruction to the device.
A programmable display device, which in general has a graphical display function, is capable of displaying an image prepared in advance to include a switch, an indicator lamp, a meter and the like, and thus serves as an operating terminal in a control system. In such a control system, it is the programmable display device provided near each device that displays an operating condition and the like of the device and that provides a control instruction to the device.
A programmable display device typically stores data on images to be displayed with use of a graphical display function on a flash memory (such as a flash erasable and programmable ROM) built in the programmable display device, such a flash memory being not easily detachable.
Thus, in a case where a user wants to use the same or similar image data at a plurality of programmable display devices (that is, the user wants to copy the image data), there has been a need for the user to transfer data via a device other than those programmable display devices. For instance, there has been a need for the user to take a procedure of uploading image data stored on a programmable display device to a device other than the programmable display device with use of dedicated software and then downloading the uploaded image data to another programmable display device with use of the same software.
A programmable display device may, instead of taking the above procedure, alternatively be arranged to store image data on a detachable external storage medium for ease of copying the image data and using the image data at another device. This arrangement makes it possible to (i) detach an external storage medium from a programmable display device and attach the external storage medium to another device or to (ii) easily copy image data stored on an external storage medium onto a general-purpose computer or the like. The above arrangement, however, involves the risk of a third party, other than the user, taking away the external storage medium or copying image data on the external storage medium for unauthorized use.
To limit access to data obtained in an unauthorized manner as described above, there has been developed a technique for placing a limit on which device is permitted to use the data. Patent Literature 1, for example, discloses a technique of (i) storing a device setting file together with data on each of a plurality of storage mediums which device setting file contains the MAC address of a terminal and the serial number of the storage medium in association with each other and (ii) in a case where the terminal reads out the data, referring to the device setting file on the basis of the MAC address of the terminal.
Patent Literature 2 discloses a technique of (i) storing, on a recording device, a file encrypted with use of a cryptographic key on the basis of the unique identifier of an electronic information device and (ii) in a case where the encrypted file is read out from the recording device, decoding the file with use of a cryptographic key regenerated from the unique identifier of a device reading out the file.